Study On Applying Coagulation-PAC Adsorption-Microfiltration Process For Backwash Water Treatment And Membrane Fouling

As water source quality gets worse and drinking water quality standards becomes stringent, the membrane process is well concerned in drinking water treatment. Membrane process for drinking water production has many advantages, such as superior water quality, less footprint, simple flowchart and high automatization, but the disposal of membrane backwash water has gained more attention.Membrane backwash water from two pilot-scale reactors was used as raw water. A coagulation-PAC absorption-microfiltration system was studied to treat discharged backwash water. Two pilot-scale coagulation-membrane filtration reactors have been operated stably in Yangliuqing Water Treatment Plant in Tianjin. Submerged microfiltration membrane and pressurized ultrafiltration membrane were used separately. Quality of the backwash water and treated water was studied. By observation of the surface of the membrane, evaluation of the recovery effect of the membrane flux with various cleaning methods and analysis of the component of the cleaning liquid, characteristics of membrane fouling and its cleaning in this process were also studied.The results show that, the quality of the treated water can meet the requirements of Standards for Drinking Water Quality (GB 5749-2006). In addition, the device is compact with short retention time, simple process and an effective way for improving drinking water producitivity. The results of submerged microfiltration membrane backwash water treatment showed that turbidity, organics and microorganisms in the backwash water were removed efficiently. During the whole operation, the average turbidity, CODMn and UV254 of the backwash water were 6.25 NTU, 6.33 mg/L and 0.050 cm-1 respectively, while those of the treated water were 0.08 NTU, 2.15 mg/L and 0.028 cm-1 respectively. Pressurized ultrafiltration membrane backwash water treatment system was influenced by filtration time of the pilot-scale reactor. When proper dosage of FeCl3 and powdered activated carbon (PAC) was added into the system, the quality of the treated water can meet the requirements of the water quality standards.The results of membrane fouling and its cleaning test show that the fouling on the surface of membrane was formed by the interreaction of inorganic and orgnic matters. Alkaline cleaning could remove most of the organic foulants, while acid cleaning was more marked to remove the inorganic foulants. The majority of soluble organic foulants on the membrane surface had low molecular weight, and iron was the major inorganic element. The pretreatment of coagulation can effectively reduce the membrane fouling, the higher coagulant dosage used, the better membrane permeability reached within the test range. Adding PAC to the system enhanced the removal efficiency of organic pollutants, remakably exended the working time in a cycle and reduced the frequency of chemical cleaning.